Cold emulsion camera

ABSTRACT

A cold emulsion camera in which the film is gripped between an optical plug and a metallic plate, which is reduced to a very low temperature by dry ice, for example. The optical plug, which may be of optical glass, is sufficiently thick to serve as an insulator for preventing frosting of the outer face of the plug. The clamping action of a metal plate against the inner end of the plug with the interposed film prevents frosting in this region.

v 0 United States Patent [151 3,667,358 Williams, Jr. et al. 1 June 6, 1972 [54] COLD EMULSION CAMERA 2,573,278 10/1951 Rowe et al. 95/37 Inventors: William D Williams Jr. 2 Heather Lane 2,787,942 4/1957 Edwards, ..95/37 Manwah NJ. 07430 Scott Usher, 98

Primary Examiner-Samuel S. Matthews Copley Avenue Teaneck 07666 Assistant Examiner-Robert P. Greiner [22] Filed: Jan. 5, 1971 Attorney-Malcolm W. Fraser [21] App]. No.: 103,981 [57] ABSTRACT A cold emulsion camera in which the film is gripped between U.S. Cl. an optical plug and a metallic plate which is reduced to a very low temperature by dry ice, for example. The optical plug, [58] Fleld of Search ..95/1 1 R, 37, 96/45 which may be of optical glass, is Sufficiem'y thick to serve as an insulator for preventing frosting of the outer face of the [56] References Cited plug. The clamping action of a metal plate against the inner UNITED STATES PATENTS end of the plug with the interposed film prevents frosting in this region. 3,110,593 11/1963 Yule ..355/17 UX 3,515,046 6/1970 lppolito et a1. ..95/1 1 R 6 Claims, 1 Drawing Figure 1. IGHT Team SECOND/ARV 1'11 RROR'. FOE REFLECTWGWPE WELQSQQPE o 0 a u u v u o v INVENTOR. bJnJJAM D. WILLIAMS J2.

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L IGHTVRQm SEQQNDARQ TLElSQQPE PATENTED 6 COLD EMULSION CAMERA BACKGROUND OF THE INVENTION from three to 12 times are reportedly achieved when these are expressed in terms of exposure time to obtain equivalent photographs, with and without cold emulsion techniques.

Thus, it would appear that cold emulsion photography would be used widely both by amateur and professional astronomers and hobbyists. However, there are relatively few cold emulsion cameras in use, and those are used routinely to produce excellent results as published in scientific papers, national journals, etc. One formidable problem facedby owners of cold emulsion cameras is the simple'fact of condensation and frosting of the films, lens and'camera. Frosting of the film or lens makes photography impossible, and frosting of the equipment prevents rapid succession of photographs which is quite desirable in many instances. Other important problems relate to the prevention of the frost; the need for relatively sophisticated equipment and techniques; and the loss of time between exposures. For example, an astronomer will plan and wait for months for the right sky position of an object and then must wait further for a clear night to photograph. Time is very precious when the particular night arrives and relatively few exposures can be made each night with the existing cold cameras. i Y

Cold emulsion cameras presently in use cope with the major problem of condensation and frost by exposing the internal face of the "optical window as well as the film under vacuum. Inlocations-of low humidity, dry air replaces the vacuum in the enclosed chamber. Such techniques appear to work satisfactorily and the published photographs attest to the quality of the cameras and the capability of the photographer. However, prior cameras have disadvantages because of the requirement for air drying and circulating equipment with its accompanying high cost; difficulty in achieving perfect seals on all joints and connections; interference with delicate tele scopic guiding operation due to vibrations, additional weight, etc'.; and inconvenience in moving the entire camera equipment. A further disadvantage resides in .the condensation and frosting of the special window and film of the entire assembly when'it all ischanged from high vacuum to atmospheric pressure between exposures. As a consequence, the equipment against the film, forming a sandwich with the film and theface of the plug. The metal plate is made cold by contact'with suita ble refrigeration means, such as solid'CO, (dry ice), or liquid nitrogen.

BRIEF DESCRlPTlON or -ma DRAWING The FlGURE is a vertical sectional elevation, somewhat schematic, of a cold emulsion camera'emb'odying the invention, a fragment of a reflecting type telescope being indicated.

DESCRIPTION OF THE PREFERRED EMBODIMENT '11 also provides. an intemal-ledge 14 against which the outer end of an optical plug 15 rests.- The optical plug 15 consists either of a solid piece of clear optical glass or suitable plastic material having a high light transmittance and little light distortion, such as polymethylmethacrylate well known examples of which are LUCITE or PLEXIGLAS. The opposite or inner and 'outer faces of the optical plug are ground and polished flat and parallel to each other. The thickness of the plug between the parallel inner and outer faces is such that the outer face remains at ambient temperature during the time period of the maximum expected exposure, despite the ex tremely low temperature at the inner face. The thickness of the plug is such that the outer parallel face of the plug is insulated againstfrosting for the expected length of time for the exposure. In practice, it is found that an optical plug of a thickness of 1% inches is satisfactory for astronomical photographs up to approximately 1 hourexposure time.

Extending into the open rear end of the camera body is'a cold box 16 having an open top or upper end. The bottom of the box is formed by a relatively thin flat plate 17 of brass or other suitable material for conducting the heat away from the film, the outer surface of which faces the inner flat face of the optical plug 15 and is ground so as to be flat and smooth to secure good contact engagement between the plate 17 and the adjacent face of the plug 15. The side wall of the cold box is must be warmed and dried to make ready for the next exposure.

SUMMARY OF THE INVENTION mechanism of any kind are required. A feature of this invention is the use of an optical plug in the form of a solid piece of clear optical glass or the like as a means of insulation to prevent frosting. The thickness of the optical plug is such that the warm (ambient temperature) face of the plug remains at ambient temperature during the time period of maximum expected exposure.

The film for the. camera is pressed firmly and directly against one face of the optical plug with the emulsion side against the plug. A flat, ground metal plate is pressed tightly formed by a'continuous metal plate 18, the bottom edge of which is welded or brazed to the upper surface of the plate 17. On the outer side of the wall 18 is thermal insulation cloth 19 of any suitable material. A ring 20 having a flat upper surface is secured to the upper end' of the wall 18 in any suitable manner.

In engagement with the upper surface of the ring 20 of the cold box is a hold down ring 21 apertured loosely to receive screw threaded rods 22 and 23, which are fixed at their lower ends to the camera body 10. At their upper ends the screw rods receive coil springs 24 and pressure nuts 25 for exerting pressure through the cold box 16 against the plate 17 to hold it firmly against the optical plug. 15.

Welded to the center of the plate 17 on the inner side thereof is an outwardly extending screw rod 26 which extends freely'through the center of a pressure plate 27, which has urirestricted movement in the cold box. A coil spring 28 is interposed between the upper face of the pressure plate 27 and a pressure regulating nut 29, which is'in screw threaded engagement with the rod 26.

The cold box 16 receives a, quantity of solidified carbon cal plug 15. It is found that such pressure does not cause pressure exposure" even upon the application of several times the pressure required to prevent frosting. Reliance is made upon the sandwich of film between the optical plug and the cold metal plate 17 to prevent the frosting of the film and the optical plug face which is in direct contact with the film.

It is found that low intensity light which finally reaches the film after passage through the optical plug 15, is not reduced in intensity enough to affect exposure because most light is lost at the lens-air interface, not in the transmitting of the light through the optical plug. Over ninety percent light transmission is possible.

It will be manifest that the camera eliminates the necessity for vacuum or other specially processed air, gas or liquid and the associated complexities and expense involved. This camera can be put in use quickly, and only a short preparation time of equipment is required between exposures by the use of 1 multiple solid optical plugs 15 which are readily interchangeable. Although the camera has been described in the field of astrophotography, it can be useful in otherfields of photography where most efficient use of extremely low light levels is important.

What we claim is:

1. A cold emulsion camera for exposing photographic film to light while maintaining the film at a reduced temperature comprising:

A. optical plug means of a transparent material of low thermal conductivity, said plug means having:

I. a first surface means which is planar;

2. a second surface means removed from the first surface means a distance such that when the first surface means is cooled, the temperature of the second surface means is not reduced below the point at which atmospheric water vapor condenses thereon during the period of photographic film exposure;

B. a clamping plate having a planar surface positionable parallel to the first surface means of the optical plug; C. means for clamping photographic film between the planar surface of the clamping plate'and the planar surface of the optical plug;

D. means for refrigerating the clamping plate.

2. A cold emulsion camera as claimed in claim 1 in which said optical plug means is of optical glass having opposite faces flat and parallel to each other.

3. A cold emulsion camera as claimed in claim 1, in which the optical plug means is a thickness of the order of 1% inches.

4. A cold emulsion camera as claimed in claim 1, in which the optical plug means consists of polymethylmethacrylate.

5. A cold emulsion camera as claimed in claim 1, in which said clamping plate constitutes the bottom wall of cold box for dry ice.

6. A cold emulsion camera as claimed in claim 1, comprising means for mounting said optical plug for enabling same to be readily removed for replacement purposes.

a 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION,

Patent 1%, 3,667,358 Dated January 6, 1972 Inventor(s) William D. Williams, Jr. et. a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On'the cover sheet, {721 "Manwah, N.J."' should read NQJ. O

Signed and sealed this l2th1d ay of D ecember l972;

SEAL) Attest:

EDWARD M.FLETCHER,JR. 7 ROBERT GO'I'TSCHALK Attesting Officer, Commissioner of Patents FORM PO-IOSO (10-6 USCOMM-DC 60376-P69 U.S. GOVERNMENT HUNTING OFFICE i969 0-366-334.

Patent No. 3,667,358 Dated January 6, 1972 Invent0 (s) William D. Williams, Jr. et. a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, [721 "Manwah, N.J. should read Mahwah, N.J.

Signed and sealed this 12th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.' ROBERT GOT'ISCHALK Attesting Officer, Commissioner of Patents FORM PC4050 H0459) uscoMM-oc scan-p09 Q .5v GOVERNMENT PRINTING OFFICE 2 I989 -355-334. 

1. A cold emulsion camera for exposing photographic film to light while maintaining the film at a reduced temperature comprising: A. optical plug means of a transparent material of low thermal conductivity, said plug means having:
 1. a first surface means which is planar;
 2. a second surface means removed from the first surface means a distance such that when the first surface means is cooled, the temperature of the second surface means is not reduced below the point at which atmospheric water vapor condenses thereon during the period of photographic film exposure; B. a clamping plate having a planar surface positionable parallel to the first surface means of the optical plug; C. means for clamping photographic film between the planar surface of the clamping plate and the planar surface of the optical plug; D. means for refrigerating the clamping plate.
 2. a second surface means removed from the first surface means a distance such that when the first surface means is cooled, the temperature of the second surface means is not reduced below the point at which atmospheric water vapor condenses thereon during the period of photographic film exposure; B. a clamping plate having a planar surface positionable parallel to the first surface means of the optical plug; C. means for clamping photographic film between the planar surface of the clamping plate and the planar surface of the optical plug; D. means for refrigerating the clamping plate.
 2. A cold emulsion camera as claimed in claim 1 in which said optical plug means is of optical glass having opposite faces flat and parallel to each other.
 3. A cold emulsion camera as claimed in claim 1, in which the optical plug means is a thickness of the order of 1 3/4 inches.
 4. A cold emulsion camera as claimed in claim 1, in which the optical plug means consists of polymethylmethacrylate.
 5. A cold emulsion camera as claimed in claim 1, in which said clamping plate constitutes the bottom wall of cold box for dry ice.
 6. A cold emulsion camera as claimed in claim 1, comprising means for mounting said optical plug for enabling same to be readily removed fOr replacement purposes. 